It lay in the central parts of the Misty Mountains, tunnelled and carved through the living rock of the mountains themselves. By the Second Age a traveler could pass through it from the west of the range to the east.

There, in the caves above, Durin and his people started the delving and building of the Great Gates of Khazad-dûm, and the First Hall leading to a bridge over a chasm. From there began the expansion, both to Levels above and to Deeps below, and mines expanding out from the inhabited areas of the city proper.

Durin the Deathless thus became King Durin I of Khazad-dûm and ruled for many years until he was named "Durin the Deathless" until he died during the First Age. Afterwards, other rulers of Khazad-dûm were sometimes named Durin, as they were considered to be his reincarnations, who the dwarves believed came to live again among his people.[2]

As the centuries passed, the descendants of Durin sat upon the throne of Khazad-dûm, and their cavernous city, that was the greatest of all their mansions, and became famous even to the distant west; the Elves of Beleriand, heard its rumour from the Dwarves of the Blue Mountains on their borders.[3]

In c. 40 of the Second Age after Beleriand was destroyed by the War of Wrath, most of the Dwarves of Nogrod and Belegost began leaving en masse from their now ruined cities for Khazad-dûm. The city was enriched not just in numbers, but in the western Houses' skills in smithing, crafting and masonry. All these factors created a renaissance for Khazad-dûm, and brought its prosperity to its zenith.

Also fleeing the destruction, the Noldor founded a country of their own by the western gate of Khazad-dûm, Eregion. A rare friendship sprang up between the Dwarves and the Elves of this new land. By that time, Khazad-dûm had expanded so much that it completely traversed the Mountains from east to west, ending to the western rocky cliffs at their base, the Walls of Moria.[4]Narvi with Eregion's ruler, Celebrimbor, constructed the magical West-gate of Moria, and indeed Celebrimbor went so far as to present King Durin III with an Elven Ring of Power.[2]

The friendship of Khazad-dûm and Eregion came to a sudden end, however, in S.A.1697. Sauronoverran the country of the Elves, and despite the best efforts of the Dwarves to help them, he succeeded in destroying Eregion and driving away the survivors. Durin sent a great force of Dwarves to protect the Doors of Durin, but with the Elves dead or fleeing far away his warriors withdrew and the gates to the city were shut against Sauron, also secluding the kingdom off from the outside world.[5]

It was also during this time that the Orcs reinvaded the mountains and made war on the Dwarves, takingMount Gundabad from the Kingdom of Durin.

Their seclusion was broken for a time with the beginning of the War of the Last Alliance. The Dwarves of Moria fought alongside the Elves and Men in their campaign to defeat Sauron for the last time.[6] With the conclusion of the war the Dwarves went back to their country, and resumed their seclusion from the world.

During this time Khazad-dûm further expanded its treasures, but despite this its numbers began to dwindle. Most of its great wealth was based on the Mithril that was found in its mines, and as the centuries passed, the Dwarves mined deeper and deeper for the precious metal. In the year T.A.1980, they dug too deep, and unleashed a nameless terror from the depths beneath the city. The creature wreaked dreadful destruction, and in slaying the King, Durin VI, became known as Durin's Bane. In the following year, Durin's son, Náin I, was also lost, and the Dwarves fled their ancient home.

After millennia as one of the richest cities in Middle-earth, Khazad-dûm stood dark and empty, but for the brooding menace the Dwarves had released. In that time it was given a new name, Moria, the Black Pit.

The monster - a Balrog of Morgoth, as was later known - lurked alone in Moria for nearly five hundred years. After that time, the old city of Khazad-dûm began to be peopled again, but not by Dwarves. Orcs from the North began to enter the abandoned city to raid its treasuries, and occupy it. They also began to worship the Balrog as their deity. Soon afterwards, Sauron directed his creatures there, and Moria began to fill with Orcs and Trolls from Mordor. Though the orcs' numbers were greatly reduced in the Battle of Nanduhirion, fought in the valley beneath Moria's East-gate in 2799, the Balrog could not be bested, and Khazad-dûm remained a place of darkness.

At some point between 2845 and 2950 the WizardGandalf entered the city looking for King Thráin II who had disappeared on journey to Erebor.[7]

In 2989, there was an attempt by the Longbeards to reclaim their ancient home. The expedition was led by Balin, who had accompanied Bilbo Baggins on the Quest of Erebor. He led a colony of Dwarves there from Erebor. The Colony was successful at first, killing a considerable number of Orcs, taking many of the Eastern halls and finding many lost treasures such as Durin's Axe. They were however defeated and slain by the Orcs in 2994.

Possibly at some point after this Aragorn Chieftain of the Dúnedain entered Moria for some unknown purpose.

When Frodo Baggins set out from Rivendell with the Fellowship, they at first planned to travel over the Misty Mountains. When they were stopped by heavy snow on Mount Caradhras, they found themselves pursued by wolves and Orcs, and fled into Moria, so as to go under the mountains. There, they found Balin's journal in the Book of Mazarbul and learned the fate of his expedition. They were then set upon by a host of Trolls and Orcs, and they discovered that the terror was, in fact, a Balrog of Morgoth. Gandalf fought the Balrog on a narrow bridge and succeeded in destroying a section of bridge to make the Balrog fall. As it fell, the Balrog snagged Gandalf's leg with its whip of thongs and pulled him after it, sending them both plunging into the abyss spanned by the bridge. The rest of the Fellowship managed to escape Moria and reach Lórien mostly unharmed.

Unknown to the Fellowship, both Gandalf and the Balrog survived the fall and fought a ferocious battle from the depths of Moria to the mountains above, demolishing the top of the legendary Endless Stair and a part of the surrounding mountain peak in the process. Gandalf cast down the Balrog upon the mountainside and lived just long enough to see it die, but his story was not yet ended.

While Gandalf had felled the Balrog, Moria remained a place of evil creatures until the Fourth Age.[8]

Though little information is given, the retaking of Khazad-dûm by Durin VII seems to have occurred during the Fourth Age. He became King of Durin's Folk, and led a final return to the city. He was successful, and long after the War of the Ring, the Dwarves of Durin's line reclaimed their inheritance, and the hammers rang again in their great halls beneath the Misty Mountains until the race of Dwarves ended.

Khazad-dûm was a huge array of chambers, passages, mines, halls, stores and pits. In general, areas were either classed as mines or city. The mines were working sections of Khazad-dûm whilst the city was the area of habitation.

The city areas of Khazad-dûm were clustered primarily to the east; these were the oldest parts of the kingdom and had access to the Great Gates. They were structured into seven Levels and seven Deeps. The Levels stretched above the gate whilst the Deeps were set deeper within the mountain below the level of the East-gate. It is possible that the First Level (on which the Great Gates were set) and the First Deep were highly intertwined.

The eastern section of the city spaces had also been delved in such a manner as to have light shafts to illuminate their chambers. One example of this is the Chamber of Mazarbul which was located on the eastern edge of the Seventh Level.

The mine areas of Khazad-dûm were interlaced with the city spaces, but spread also westward toward the Doors of Durin. The mines ran deeper and further than any other tunnels within Khazad-dûm, and it is possible that more of the lower Deeps were given over to mining, although this is only conjecture.

The defined change between mines and city can be seen when the Fellowship pass through Moria - there is a marked difference between the early passages and chambers and those of the city structures illuminated by Gandalf.

Far below Moria, there are abysses, spaces and tunnels not known even by the Dwarves, but known by the Balrog. Unknown beings gnaw the earth and make them, far from the knowledge of any lore.

The name Khazad-dûm in Khuzdul means "Dwarves' Mansion(s)". Khazâd being the plural of khuzd "Dwarves" while dûm (or possibly rather tûm) a word for "excavation(s), hall(s), mansion(s)" (it is not clear if the second word is in singular or plural form).

The Elves translated it as Casarrondo (Quenya, name given by the Noldor)[11] or Hadhodrond (Sindarin). The word Hadhodrond is composed of the elements hadhod (an attempt by the Elves to render Khazâd, (the Dwarves' name for their own kind, into Elvish sounds) + rond ("cavern").[source?]

Phurunargian meaning "Dwarrowdelf" or "Dwarf-delving" was the Westron name for Khazad-dûm.[12][13] The word derives from the root PHUR ("to delve") and narg- ("dwarf").[13]Tolkien noted that the form Phurunargian was "archaic" Westron although he did not mention the elements that make it archaic (over a possible vernacular form).[14][12]

The entire journey through Moria takes place in one level, which can be completed in several minutes. The iconic location are portrayed immediately next to each other and in the end, Gandalf defeats the Balrog and continues journey with the Fellowship.

Mines of Moria was the first major expansion of the game, released in November 2008. Almost the entirety of Moria is present in the game, with players able to freely journey from the West Gate to the East Gate and from the Cliffs of Zirakzigil to the very Foundations of Stone where nameless things dwell.

Moria is divided into several major sub-areas, depicted on the map to the right. The Great Delving lies directly next to the West Gate and links ancient Dwarven mines to palaces, academies and foundries founded during Khazad-dum's glory days. Durin's Way is the area, where, according to legend, Durin himself first braved the mines before bringing his folk in there. Zelem-Melek is home to both numerous Orc encampments and the famed Twenty-first Hall. Silvertine Lodes refers to the mining area located directly under Silvertine, much like the Redhorn Lodes are the mining area under the peaks of Redhorn. The Water-Works hosts both a large underground lake and ancient Dwarven gears, wheels and devices that delivered the fresh water throughout the whole kingdom once. The Flaming Deeps is an area that reeks with fire and where few could survive for long - it appears that Durin's Bane resided there following his reawakening. Nud-Melek mostly consists of the Second Hall and the First Hall. The Foundations of Stone are located below the deepest delving of the Dwarves; no light has ever shined there and, as Gandalf recounted, nameless creatures older than the world gnaw at the roots of the mountains.

Surprisingly for those seeing it for the first time, Moria in The Lord of the Rings Online is very much inhabited. In an original storyline by Turbine, Dwarves from the Iron Hills sent by Dáin Ironfoot arrive in Moria shortly after the Fellowship to learn the fate of Balin's expedition. With Durin's Bane recently gone, the Orcs and Goblins of Moria are in great disarray, which allows the Dwarves to move in and establish encampments at all major crossroads. Fresh supplies are coming from both East and West gates, preventing the Iron Hill Garrison from being cut off like Balin was. However, the developers noted that they aware that Moria wasn't re-colonized until the Fourth Age in canon, meaning that at some point in the future of the game the Iron Garrison may be forced to leave the mines.